I. Field
The present invention relates generally to circuits, and more specifically to a voltage controlled oscillator (VCO) with temperature compensation.
II. Background
VCOs are an integral part of many electronics circuits and are particularly important in communication circuits. For example, VCOs are often used to generate local oscillator (LO) signals, which are used by transmitter and receiver subsystems for frequency upconversion and downconversion, respectively. VCOs are also used to generate clock signals for synchronous circuits (e.g., flip-flops). A wireless device (e.g., a cellular phone) in a wireless communication system may employ multiple VCOs to generate LO signals for transmitter and receiver circuitry and clock signals for digital circuitry.
A VCO typically employs one or more variable capacitors (varactors) to allow for adjustment of the frequency of oscillation for the VCO. The tuning range of the VCO refers to the range of oscillation frequencies achieved by varying the varactors. The tuning range is used to (1) ensure that the VCO can operate at the required frequency or range of frequencies and (2) compensate for changes in oscillation frequency due to component tolerances, integrated circuit (IC) process variations, and so on.
The circuit components of a VCO normally change with temperature. Consequently, the oscillation frequency of the VCO typically drifts with variation in temperature. For many applications (e.g., wireless communication), the temperature dependent frequency drift is a concern and is accounted for by designing the VCO with extra tuning range to cover this frequency drift. The extra tuning range may degrade the phase noise performance of the VCO. Phase noise refers to short-term random frequency fluctuations of an oscillator signal and is a parameter used to describe the quality of the oscillator signal. If the temperature dependent frequency drift can be reduced or minimized, then it may be possible to improve the overall performance of the VCO.
There is therefore a need in the art for a VCO with temperature compensation.